She was born in Cerritos, CA and has lived there her whole life with her family. Her parents were born in Korea but immigrated to the U.S. in their teens. They live a less traditional Asian lives than others.

The superstition:

If you wash your hair at night after you study, everything you memorized and learned up till then will be lost.

She also repeated the text in Korean for me:

공부하고 자기전에 머리를 가므면 외운거 다 지워진다, 잊어버려. 그거야 그냥 장난이지.

The Analysis:

This story was told to my friend before her big exam when she was in middle school. It is analogous to the idea that washing her hair will also wash out everything in her head that was stored up till that point. She says that the story was told by her mother, who had then heard it from her mother back in Korea. An insight that I gained was the Korea is surrounded by water. Korean life is also dominated by water, with rivers and the ocean. It is a possibility that this saying sprung up due to the Korean affinity for water, which later might have turned into a repulsion of so much water.